A -compact topological space is a topological space that is the union of countably many compact subsets.
Sigma-Compact Topological Space
See also
Compact Subset, Topological SpaceThis entry contributed by Mirko Hessel
Explore with Wolfram|Alpha
Cite this as:
Hessel, Mirko. "Sigma-Compact Topological Space." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/Sigma-CompactTopologicalSpace.html